The disposal of wastes both from municipal and industrial sources, such as trash, rubbish, garbage, animal wastes, agricultural wastes, and waste of plastic processing operations, is rapidly becoming of immense national concern. The cost of disposal ranks third behind public schooling and highways as municipal expense in the United States.
It is estimated that each individual in the country generates between 4 and 6 pounds of waste per day, that the industrial output is equivalent to approximately 5 pounds of solid waste per person per day. Previous methods of mass waste disposal, such as landfill, are becoming impossible while others such as incineration are costly and result in air pollution problems.
A vast majority of the waste which is presently disposed of contains products which are immediately recyclable back into the economy or products into which the waste can be converted for recycle back to the economy. Directly recyclable constituents are the various metals present, such as aluminum and steel, and glass. For the most part, the organic fraction of the waste is subject to a flash pyrolysis operation following recovery of the directly recyclable inorganic fraction. Flash pyrolysis yields char, a pyrolytic gas and a pyrolytic oil as products.
A particularly attractive method for converting the solid organic wastes into new and useful products consists of a process where the waste material is first dried and comminuted to a particle size wherein the largest particle has a maximum particle dimension of less than about 1 inch. There is then formed a turbulent gas stream by admixing the dried comminuted waste material with hot char and a carrier gas which does not deleteriously react with or oxidize the organic waste materials or products derived therefrom. The mixture is passed through a flash pyrolysis zone where at a temperature between 600.degree. and 2000.degree. F. the organic waste undergoes flash pyrolysis yielding solid char and a vaporized hydrocarbon constituent. The vaporized hydrocarbon constituent is separable as a pyrolytic oil and a normally gaseous hydrocarbon constituent which may be recycled to the process as a carrier gas or conveying gas. Preferably, valuable constituents such as olefin are first removed from the gaseous product. A portion of the char is also recycled as the heat source.
The pyrolytic oils formed, while varying in nature depending upon the composition of the waste material processed and pyrolysis conditions employed, are at the same time unique. They may be characterized as an oxygenated, complex organic fluid, typically up to 40% and in some cases up to 85% soluble in water, acids or base. Solubility in polar organic solvents such as glycerol is limited and the pyrolytic oils are relatively insoluble in non-polar organic solvents, such as diesel oil, carbon tetrachloride, pentane, decane, benzene, toluene and hexane. The pyrolysis oil, however, can be successfully blended and mixed with various No. 6 fuel oils. Combustion stability of the mixture is about the same as No. 6 fuel oil alone.
An example of an elemental analysis of a pyrolytic oil that is obtained from the pyrolysis of a waste material containing about 70% cellulosics is as follows: up to about 60% carbon, from about 5 to about 10% hydrogen, up to about 2% nitrogen and from about 20 to about 40% oxygen. The empirical formula which best fits the pyrolytic oil analysis is C.sub.5 H.sub.8 O.sub.2. Specific gravities are unusually high, ranging from 1.1 to about 1.4.
The hot gases containing the pyrolysis products must be quenched from the high temperature of the flash pyrolysis zone down to temperatures of approximately 300.degree. F. or lower, preferably to approximately 200.degree. F. or lower. At the same time the velocity of the vapor stream is reduced. The combination of reduced temperature and reduced velocity causes the liquid and solid constituents to condense and drop out of the vapor stream. The quenching liquid is normally introduced into the vapor stream just before or after it enters the knockout pot. However, in the past the quenching of the vapor stream by a cooling liquid has caused severe plugging in the piping adjacent the inlet of the quench liquid.